3 ms·

> I don't see how that's going to be electrified. And I'm not talking in the sense of "technology isn't there yet", but more like "the laws of physics wouldn't

> I don't see how that's going to be electrified. And I'm not talking in the sense of "technology isn't there yet", but more like "the laws of physics wouldn't appreciate that". Well, good news! The laws of physics don't really care (at least not directly). See, scale occurs nowhere in the range equation: https://en.wikipedia.org/wiki/Range_(aeronautics)#Electric_aircraft https://en.wikipedia.org/wiki/Range_(aeronautics)#Electric_a... No matter how much it's repeated, scale still doesn't matter in terms of the physics of flight and electrification. I know people find it counter-intuitive, but it really ISN'T harder from a physics perspective to electrify a 737 (although you generally want a longer wingspan than airports like, so you may choose 777x-like extending wingtips). Pet peeve of mine that people think "oh, it's big so it's hard to electrify" (without actually doing any fundamental physics on the idea) when the largest machines are actually already electric (think bucketwheel excavators). In fact, in some ways, efficiency IMPROVES with scale, but it depends on a few factors (may need truss-braced wings at long enough wingspan, but that's doable). See how L/D improves with increasing Reynolds Number: https://www.researchgate.net/figure/Lift-to-drag-ratio-variation-with-Reynolds-number-reproduced-from-73_fig1_258378934 https://www.researchgate.net/figure/Lift-to-drag-ratio-varia... I mean ask yourself: is a business jet much more efficient than a 737? No? Well then why would it be harder to electrify a 737, from a physics perspective? In fact, a 737 is far more efficient than most much smaller aircraft using jet technology. And a Cessna is like half as efficient (or less) in terms of L/D in spite of being slower and much smaller.

missedthecue 5y ago
Even with the highest theoretical possibilities, batteries cannot be as energy dense as kerosene. Kerosene has about about 12,000 Wh/kg, a cutting edge lithium battery has only 200. Scientists speculate that on paper, chemical batteries can theoretically get to about 1100 Wh/kg. A perfect world is still not even close to close to kerosene. Batteries do not get lighter as they discharge like a fuel tank does, meaning a huge efficiency loss. Finally it's simply not physically possible to recharge a large airliner size battery as fast as a fuel tank can be refilled, and on short haul flights, turnaround matters. Some airlines go from arrival to departure in 30 minutes. Modern airliners do up to 8 flights a day!
- Robotbeat 5y ago
  > Even with the highest theoretical possibilities, batteries cannot be as energy dense as kerosene. So what? We can make kerosene-fueled aircraft that can fly more than all the way around the world without refueling. In fact, we did it 15 years ago, and we left some performance on the table as it had a L/D of 37 but modern sailplanes can get over 70 L/D (and the jet engine they used wasn't particularly efficient), and with forced laminar flow control, 100 L/D is possible. https://en.wikipedia.org/wiki/Virgin_Atlantic_GlobalFlyer https://en.wikipedia.org/wiki/Virgin_Atlantic_GlobalFlyer Kerosene is better than it needs to be. Cutting edge typical lithium ion chemistries (like you might find in a Tesla) has about 300Wh/kg, but pre-production lithium-sulfur batteries can get up to 650Wh/kg (lithium sulfur and lithium metal anode batteries that are available in sample quantites in actual pouch form are around 400-450Wh/kg). But also, batteries are roughly twice (sometimes 3 times) as efficient as jet engines. As you mention, chemical batteries could do 1100Wh/kg (not counting lithium-air, which could do much, much better but we're probably a couple decades to deploying them). Not getting lighter over time is a performance drag, but there are actually ways to deal with it. But let's split the difference and say batteries could be about a tenth as good as kerosene. 41,000km is the distance that Globalflyer flew. A tenth that range is 4100km, which is the minimum flight length to qualify for long-haul (and also the distance from Hawaii to California). So we could have long haul electric flight if we wanted to, without the solar-electric trick or any kind of towing, in-air charging, staging, or launch-assist. Turnaround in 30 minutes isn't fantastically hard for battery chemistries, either, BTW. 5 minutes would be pretty hard, although still not impossible (and some chemistries can do this). And again, this is largely scale-invariant. A Tesla that can mostly charge in 30 minutes means a short-haul aircraft could as well. And you can get lithium batteries (LiPo and Lithium Titanate) that charge in 6-12 minutes or so (5-10C rate). This is faster than most jets get refueled (it takes 45 minutes to an hour for larger jets, so I don't see charging time to be a huge challenge).
  - missedthecue 5y ago
    Global flyer weighed 1500kg and topped out at half the speed of an airliner's cruising speed. A 737 weighs over 40,000kg empty and tens of thousands more when you add in passengers and their luggage. Yes, electric flight is possible, but it simply cannot replace the modern airliner.

missedthecue 5y ago

Even with the highest theoretical possibilities, batteries cannot be as energy dense as kerosene. Kerosene has about about 12,000 Wh/kg, a cutting edge lithium battery has only 200. Scientists speculate that on paper, chemical batteries can theoretically get to about 1100 Wh/kg. A perfect world is still not even close to close to kerosene. Batteries do not get lighter as they discharge like a fuel tank does, meaning a huge efficiency loss. Finally it's simply not physically possible to recharge a large airliner size battery as fast as a fuel tank can be refilled, and on short haul flights, turnaround matters. Some airlines go from arrival to departure in 30 minutes. Modern airliners do up to 8 flights a day!

Robotbeat 5y ago
> Even with the highest theoretical possibilities, batteries cannot be as energy dense as kerosene. So what? We can make kerosene-fueled aircraft that can fly more than all the way around the world without refueling. In fact, we did it 15 years ago, and we left some performance on the table as it had a L/D of 37 but modern sailplanes can get over 70 L/D (and the jet engine they used wasn't particularly efficient), and with forced laminar flow control, 100 L/D is possible. https://en.wikipedia.org/wiki/Virgin_Atlantic_GlobalFlyer https://en.wikipedia.org/wiki/Virgin_Atlantic_GlobalFlyer Kerosene is better than it needs to be. Cutting edge typical lithium ion chemistries (like you might find in a Tesla) has about 300Wh/kg, but pre-production lithium-sulfur batteries can get up to 650Wh/kg (lithium sulfur and lithium metal anode batteries that are available in sample quantites in actual pouch form are around 400-450Wh/kg). But also, batteries are roughly twice (sometimes 3 times) as efficient as jet engines. As you mention, chemical batteries could do 1100Wh/kg (not counting lithium-air, which could do much, much better but we're probably a couple decades to deploying them). Not getting lighter over time is a performance drag, but there are actually ways to deal with it. But let's split the difference and say batteries could be about a tenth as good as kerosene. 41,000km is the distance that Globalflyer flew. A tenth that range is 4100km, which is the minimum flight length to qualify for long-haul (and also the distance from Hawaii to California). So we could have long haul electric flight if we wanted to, without the solar-electric trick or any kind of towing, in-air charging, staging, or launch-assist. Turnaround in 30 minutes isn't fantastically hard for battery chemistries, either, BTW. 5 minutes would be pretty hard, although still not impossible (and some chemistries can do this). And again, this is largely scale-invariant. A Tesla that can mostly charge in 30 minutes means a short-haul aircraft could as well. And you can get lithium batteries (LiPo and Lithium Titanate) that charge in 6-12 minutes or so (5-10C rate). This is faster than most jets get refueled (it takes 45 minutes to an hour for larger jets, so I don't see charging time to be a huge challenge).
- missedthecue 5y ago
  Global flyer weighed 1500kg and topped out at half the speed of an airliner's cruising speed. A 737 weighs over 40,000kg empty and tens of thousands more when you add in passengers and their luggage. Yes, electric flight is possible, but it simply cannot replace the modern airliner.